For. Snow Landsc. Res. 78, 1/2: 139–150 (2004)
139
Long-term silviculture experiments contribute to science-based
forest management in British Columbia’s public forests
Al K. Mitchell1, Alan Vyse2, David J. Huggard3 and William J. Beese4
1
2
3
4
Canadian Forest Service, Pacific Forestry Centre, 506 West Burnside Road, Victoria, British
Columbia, Canada V8Z 1M5. [email protected]
British Columbia Forest Service, 515 Columbia ST. Kamloops, British Columbia, V2C 2T7.
[email protected]
University of British Columbia, Centre for Applied Conservation Research, VBC, 2424 Main Mall,
Vancouver BC, VGT 1Z4. [email protected]
Weyerhaeuser, British Columbia, 95 Front Street, Nanaimo, British Columbia, V9R 5H9 Canada.
[email protected]
Abstract
Protests over clearcutting public forestlands have been a part of British Columbia’s forest policy
scene for the last two decades. Pressure to modify silvicultural systems has resulted in the installation of a number of long-term silviculture experiments in British Columbia. In this paper we
focus on how two of these experiments (MASS, Sicamous Creek) are being used to compare
silvicultural systems, and to test hypotheses related to the retention of forest structure and the
long-term influence of edges, aggregates and single trees on ecological processes. Results have
shown that a given silvicultural treatment can have both negative and positive impacts depending
on the values (e.g. regeneration, biodiversity, nutrient cycling) under consideration. The management influence of these experimental results are less obvious. The MASS project, as an operational demonstration, has had a substantial impact on the practices of one major company in
coastal British Columbia, but the Sicamous Creek project has yet to have any major direct impact.
We comment on the reasons for such differences, the prospects for continued funding, and lessons
learned from conducting long-term projects such as these.
Keywords: silvicultural systems, clearcut, partial cutting, edges, patch size, variable retention
1
Introduction
Protests over clearcutting public forestlands have been a part of British Columbia’s forest
policy scene for the last two decades. Recent publications such as “A cut above: Ecological
principles for sustainable forestry on BC’s coast” (DREVER 2000) from the Suzuki
Foundation and “British Columbia’s Endangered Forests: what government and industry
aren’t telling you” (ForestEthics 2003) indicate that the controversy continues. Responses
have ranged from a major overhaul of legislation, to more careful planning of opening sizes
and shapes in visually sensitive areas, to jail sentences for protesters.
The public ownership of 95% of forest lands in British Columbia is unique in the developed world. This brings a special set of problems for regulating forestry practices. The public
has brought considerable pressure to bear for the diversification of silvicultural systems.
Government has responded by introducing a results-based forest practices code. Passed in
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1994, the code contains provisions for further limiting the impact and extent of clearcutting
and provides a context for testing the feasibility of partial cutting and retention silvicultural
systems. However, little is known about the impacts such systems will have on growth and
yield, timber supply and environmental values or if the restrictions are having any effect.
Pressure to modify silvicultural systems has also resulted in the installation of a number
of large-scale experiments to test changes in forest structure in British Columbia (DAIGLE
1995; PUTTONEN and MURPHY 1997). These include Date Creek (COATES et al. 1997),
Quesnel Highlands (ARMLEDER and STEVENSON 1994), Lucille Mountain (EASTHAM and
JULL 1999), Opax Mountain (KLENNER and VYSE 1998), Sicamous Creek (VYSE 1999) and
the Montane Alternative Silvicultural Systems (MASS) Project (ARNOTT et al. 1995), in
which the operational, economic and ecological impacts of alternatives to clearcutting are
being investigated.
A premise common to all these trials is that the amount and the arrangement of retained
forest structure will affect ecological values. By retaining diverse structures representative
of the pre-harvest stand condition, including dead trees and coarse woody debris, diverse
habitats will be conserved for the variety of organisms that underpin ecosystem functions
(FRANKLIN et al. 1997, BURGESS et al. 2001). However, the links between forest structures
and ecosystem attributes have seldom been investigated (SPENCE 2001). These attributes
form the foundation of ecologically based silvicultural systems as advocated by FRANKLIN
et al. (1997) and LINDENMAYER and FRANKLIN (2002). Of particular interest is the comparison of ecological values under different silvicultural systems that create edges and patches
with a variety of orientations and sizes, and varying amounts of dispersed (single tree) and
aggregated (groups of trees) retention.
Because managing public forests for multiple ecological, social and economic values will
require trade-offs, it would be desirable to make decisions based on measurements of the
impacts of different silvicultural alternatives on those values. This type of science-informed
approach has been taken by Weyerhaeuser, British Columbia, in their coastal operations,
where research on the operational and economic feasibility of silvicultural alternatives to
clearcutting conducted at MASS in part gave the confidence to proceed with a plan to phase
out clearcutting and move toward retention forestry. As the pressure for third-party certification of forestry practices increases, the demand for ecologically based criteria for making
decisions about the amount and pattern of overstory retention will likely become more
acute. This knowledge is presently quite scanty for most of British Columbia’s forest types.
In this paper we focus on how two interdisciplinary long-term silvicultural experiments,
one in the coastal mountains of Vancouver Island (MASS) and the other in the south central
mountains of the province (Sicamous Creek), are contributing to the knowledge base for
forest management decisions relating to clearcutting and other silvicultural practices.
2
The montane alternative silvicultural systems project (MASS)
Located in a coastal montane forest (850 m a.s.l.) on Vancouver Island, the Montane
Alternative Silvicultural Systems (MASS) project tests three silvicultural alternatives
(Green Tree Retention, Patch Cut, and Shelterwood) and compares them with a Clearcut in
a previously uncut forest dominated by Tsuga heterophylla and Abies amabilis (ARNOTT
et al. 1995; ARNOTT and BEESE 1997). The study began in 1993, using a factorial design with
three 9-ha replicates of each of three silvicultural systems treatments and a large clearcut for
comparison (Fig. 1).
For. Snow Landsc. Res. 78, 1/2 (2004)
141
Fig. 1. The Montane Alternative Silviculture Systems (MASS) Project. Layout of silvicultural systems
treatments. (From ARNOTT and BEESE 1997).
The silvicultural systems treatments were: 1) Clearcut – A 69-ha opening made using
conventional clearcutting methods. Within the opening, three 9-ha treatment “blocks” were
selected for parity with the experimental design used in the other treatments; 2) Patch Cut –
Three 1.5-ha clearcut openings within each 9-ha treatment block; 3) Green Tree Retention –
≥ 25 trees ha-1 retained within each 9-ha treatment block; and 4) Shelterwood –
200 trees ha-1, (ca. 30% of the original stand basal area) were retained within each 9-ha
treatment block.
3
Sicamous creek research project
Located in the British Columbia interior in a subalpine forest (1550–1850 m a.s.l.), the
Sicamous Creek Research Project focuses on comparisons of opening size and the effects of
forest edge (VYSE 1999). The experiment tests different opening sizes (0.1 ha, 1.0 ha and 10.0
ha, and individual tree selection) in a cold, wet, previously uncut forest dominated by Picea
engelmanni and Abies lasiocarpa (HUGGARD and VYSE 2002b).
Five harvest treatments were applied to three 30-ha replicate units at the Sicamous Creek
site (Fig. 2): 1) 10-ha clearcut with 20 ha of leave strips, 2) nine 1-ha openings with 100-m
leave strips, 3) sixty-five 0.1-ha patch cuts with 30-m leave strips, 4) uniform individual tree
selection (ITS) removing 20% of the trees across the size distribution, and 5) uncut controls.
With roads and skid trails, each of the four harvest treatments removed approximately onethird of the trees, representing the first pass of a three-pass system.
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Al K. Mitchell et al.
Fig. 2. Aerial view and location of the Sicamous Creek Silvicultural Systems Project.
4
Applying knowledge for science-informed management of
ecological values
To facilitate science-informed forest management, the ecosystem attributes under investigation should be considered as values just as social attributes such as visual quality and
recreation potential are considered as values. The MASS and Sicamous Creek projects have
begun to quantify the short- and long-term effects of silvicultural alternatives on ecological
values related to regeneration, nutrient cycling and biodiversity. Although the silvicultural
treatments are different, they share common characteristics with respect to the creation of
edges and the influence of retained overstory in the form of single trees or groups of trees.
The idea of forest influence is at the core of retention silvicultural systems (KEENAN and
KIMMINS 1993; MITCHELL and BEESE 2002). Most commonly this is thought of as the extent
of the influence of the retained trees or stand, but the inverse concept in which the opening
has influence on the retained stand also has relevance. In other words, any opening creates
an edge and the edge effect extends into and away from the opening. The edge influence can
be measured in terms of both abiotic and biotic values. Scientific information on forest influence could be applied to address the questions of how large a patch of trees must be to have
conditions representative of the unharvested stand, and what size and shape of opening can
be made and still conserve forest influence over the harvested area.
Results from MASS and Sicamous Creek have shown that a given silvicultural treatment
can have both negative and positive impacts depending on the ecosystem attributes (values)
under consideration. Following are some examples of those impacts on regeneration, nutrient
cycling and biodiversity, and the silvicultural recommendations that would result from the
findings. These examples have been greatly simplified. They are intended as examples of
how management decisions about silvicultural systems, if based on scientific information,
could differ depending on which values are considered.
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5
Clearcuts versus retention systems
Aggregated and dispersed retention are two partial cutting systems that are being advocated
as alternatives to clearcutting, particularly in coastal British Columbia. Information collected
at the MASS site indicates that the preferred system will change depending on which set of
values (e.g. regeneration, nutrient cycling, and biodiversity) are considered.
5.1
Regeneration
Some indicators of regeneration success can be favoured by aggregated retention and
clearcut systems (PC, CC) or by dispersed systems (GT, SW), while others are favoured by a
combination of the two (Table 1). Dispersed retention systems (GT, SW) or aggregated
retention with small openings (PC) are more favourable for the establishment of natural
regeneration than large clearcuts. Although the high level of dispersed retention in the SW
promotes seedfall for natural regeneration, seedling growth rates are reduced unless shelter
trees are removed as in the traditional approach. At MASS, some or all of the SW trees will
be retained as long-term reserves, which will continue to affect growth rates. In contrast,
artificial regeneration can be successful over a wider range of approaches, including aggregated retention, clearcuts or low levels of dispersed retention (GT). For these indicators of
regeneration at MASS, aggregated and clearcut systems would be recommended for
management based on artificial regeneration, and dispersed systems would be recommended for management decisions based on natural regeneration.
Table 1. Overstory retention effects on regeneration indicators at MASS (CC, clearcut; PC, patch cut;
GT, green tree retention; SW, shelterwood), combining data for the dominant tree species (Abies amabilis; Tsuga heterophylla). Shaded cells show silvicultural systems of choice for each indicator. Source:
Beese, W.J., Sandford, J.S., Andersen, T.G. and Martin, N.J., 2000. Natural Regeneration and Vegetation
Dynamics in Coastal Montane Forests at MASS. Contract report to Forest Renewal BC, 41 p.
Indicator
CC
PC
GT
SW
Recommendation
Seedfall (seeds/square m)
Natural regeneration (% survival year 3)
Natural regeneration height (cm at year 5)
Planted seedling survival (% over 5 years)
Planted seedling height (cm at 7 years)
306
95
52
90
158
2218
89
51
97
159
2199
88
52
94
164
6661
87
39
80
115
SW
CC
CC, PC, GT
CC, PC, GT
CC, PC, GT
5.2
Nutrient cycling
Nutrient cycling processes that underpin site productivity could be changed in the short
term and perhaps in the long term by different retention systems. However, there is no indication from physiological measures of stress in regenerating seedlings at MASS that there
were major differences in stress levels among the clearcut, aggregated or dispersed systems
(Table 2). Although seedling growth was reduced in the dispersed (SW) system, there was no
indication that nutrient cycling processes were detrimentally affected resulting in seedling
stress. For these indicators, aggregated retention or clearcut systems would be recommended,
perhaps mixed with low levels of dispersed retention, for management decisions based on
nutrient cycling values.
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Al K. Mitchell et al.
Table 2. Overstory retention effects on regeneration physiology at MASS (CC, clearcut; PC, patch cut;
GT, green tree retention; SW, shelterwood), combining data for the dominant tree species (Abies amabilis;
Tsuga heterophylla). Shaded cells show silvicultural systems of choice for each indicator. Modified from:
MITCHELL 2001.
Indicator
CC
PC
GT
SW
Recommendation
Light use (Fv/Fm, year 3)
Photosynthesis (Amax, year 3)
Tree water stress (MPa, year 3)
0.74
8.4
–1.6
0.74
7.6
–1.6
0.73
8.1
–1.6
0.74
8.5
–1.6
CC, PC, GT, SW
CC, SW
CC, PC, GT, SW
5.3
Biodiversity
Using indicators of species richness and abundance, from studies of plant communities at
MASS, the dispersed SW system would be chosen for biodiversity conservation (Table 3).
Overall species diversity may increase after harvesting due to common invasive native and
non-native plants; therefore, species losses from the pre-harvest forest condition or changes
to species groups that are sensitive to disturbance may be more important indicators for
biodiversity conservation. The SW system at MASS had the fewest species losses and
maintained the greatest cover of bryophytes among treatments. The data for the patch cuts
(PC) in Table 3, however, includes only the harvested portion. If the retained aggregates
were included as long-term retention, the PC would equal or exceed the SW for maintenance
of understory plant diversity.
Table 3. Overstory retention effects on indicators of plant diversity at MASS (CC, clearcut; PC, patch
cut; GT, green tree retention; SW, shelterwood). ns = no effect. Shaded cells show silvicultural systems of
choice for each indicator. Modified from Beese, W.J., Sandford, J.S., Andersen, T.G. and Martin, N.J.
2000. Natural Regeneration and Vegetation Dynamics in Coastal Montane Forests at MASS. Contract
report to Forest Renewal BC, 41 p.
Indicator
CC
PC
GT
SW
Recommendation
Richness (number of species)
Abundance (frequency of species)
Species losses*
Bryophyte cover (%)*
ns
ns
17
9
ns
ns
27
9
ns
ns
17
11
greater
greater
9
62
SW (PC**)
SW (PC)
SW (PC)
SW (PC)
* percent of pre-harvest at year 5
** when PC retained aggregates are included.
6
Opening size
In the interior of British Columbia, particularly at high elevations, foresters have focused
more on reducing clearcut size than retention. Information collected at the Sicamous Creek
research site showed a diverse range of responses to 10-ha, 1.0-ha or 0.1-ha openings, or to
individual tree selection (ITS) when three different values – regeneration, nutrient cycling,
and biodiversity – are considered.
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6.1
Regeneration
Opening size can significantly affect different indicators of regeneration. Opening sizes of
10 ha or 1 ha tend to favour artificial regeneration, and small openings (0.1 ha) or single tree
selection systems tend to favour natural regeneration (Table 4). Results also show that
seedlings grew more slowly under the canopy of retained trees and within one tree height of
the North facing edge in openings.
Table 4. Patch size effects on some indicators of regeneration at Sicamous Creek. (ITS, individual tree
selection). Shaded cells show silvicultural systems of choice for each indicator. Source: HUGGARD and
VYSE 2002b.
Indicator
Seedfall (/m2/yr)
Natural regeneration (seedlings/ha)
Seedling survival (% over 4 years)
Seedling height growth (cm at 4 years)
6.2
10 ha
1 ha
0.1 ha
ITS
Recommendation
30
500
88
46
29
200
81
46
41
2600
77
51
73
2400
75
40
ITS
0.1, ITS
10
0.1
Nutrient cycling
In the short term, nutrient cycling was strongly influenced by opening size with significant
reductions in litterfall and increases in mineral nitrogen when the opening size reached 0.1 ha
or more. Decomposition was favoured in the individual tree selection system (Table 5).
Table 5. Patch size effects on some indicators of nutrient cycling at Sicamous Creek (ITS, individual
tree selection). Shaded cells show silvicultural systems of choice for each indicator. Modified from:
HUGGARD and VYSE 2002b.
Indicator
Mineral nitrogen (µg N/g soil)
Decomposition – needles (% loss/5 years)
Litterfall (kg/ha/year)
6.3
10 ha
1 ha
0.1 ha
ITS
Recommendation
21
51
36
22
49
34
20
52
85
10
56
415
10, 1.0, 0.1
ITS
ITS
Biodiversity
Different components of biodiversity can be significantly affected by opening size. For
example, woodpeckers or snail-eating ground beetles were favoured by all the opening sizes
markedly more than by individual tree selection. In contrast, voles and millipedes were
favoured in small (0.1-ha) openings compared with large and intermediate (10-ha or 1.0-ha)
opening sizes or individual tree selection (Table 6). Many other species studied at Sicamous
Creek benefited from small openings, but this contrasted with the better results for planted
regeneration in larger openings. Therefore, management options for maintaining stand-level
biodiversity could conflict with regeneration goals.
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Al K. Mitchell et al.
Table 6. Patch size effects on some indicators of biodiversity at Sicamous Creek. Abundances as a
percent of abundance in controls (ITS, single tree selection). Shaded cells show silvicultural systems of
choice for each indicator. Modified from HUGGARD and VYSE 2002b.
Indicator
Three-toed woodpeckers
Red-backed voles
Millipedes
Snail-eating ground beetle
7
10 ha
1 ha
0.1 ha
ITS
Recommendation
122
80
62
81
114
80
80
84
101
91
99
88
22
77
76
54
10, 1.0, 0.1
0.1
0.1
10, 1.0, 0.1
Forest influence
Retention silvicultural systems are predicated in part on the idea that the influence of the
uncut stand extends one or two tree lengths into the harvested area (FRANKLIN et al. 1997;
MITCHELL and BEESE 2002). Based on post-harvest microclimatic data from Sicamous Creek,
forest influence can be detected 25 m to 50 m (one to two tree lengths) into the forest and into
the harvested area (Fig. 3). However, forest influence on other values such as nutrients may
extend only very short distances (less than 10 m) into the cutblock (Fig. 4). This is also the case
for most components of biodiversity, such as abundance of plant species, where forest influence is also restricted to a narrow band on either side adjacent to the stand edge (Fig. 5).
The results also show that some of the attributes of nutrient cycling and biodiversity can
be negatively affected while others are positively influenced. For example, some soil nutrients such as nitrate increase dramatically at the stand edge, while others such as potassium
decrease dramatically. Similarly, plant abundance can be increased, as in the case of herbs, or
negatively affected, as in the case of bryophytes. Therefore, forest influence could extend
two tree-heights or it could extend almost no distance at all, and silvicultural systems that
create abundant edges could have negative or positive effects, depending on the values
under consideration.
Forest
Clearcut
Forest
Percent of maximum value
100
80
60
Forest floor
moisture
Wind speed
40
Diffuse light
20
0
50 25 0 25 50 75
125
125
75 50 25 0 25 50
S (E) edge
N (W) edge
Distance from edge (m)
Fig. 3. Wind speed, diffuse light, and forest floor moisture across edges. Wind speed measured across
west and east edges. Maximum value is the maximum individual point recorded along the transect (from
HUGGARD and VYSE 2002a).
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For. Snow Landsc. Res. 78, 1/2 (2004)
Forest
Percent of maximum value
100
Clearcut
Forest
80
60
Potassium
40
NO3
20
0
50
25
0
N edge
25
50
50
25
0
S edge
25
50
Distance from edge (m)
Fig. 4. Net soil nitrate and soil potassium across edges. Maximum value is the maximum individual point
recorded along the transect (from HUGGARD and VYSE 2002a).
Forest
Clearcut
Forest
50
45
40
Cover (%)
35
30
Herbs
25
Shrubs
20
15
Bryophytes
10
“Increasers”
5
Veratrum
0
50
25
0
25
N edge
50
50
25
0 25
S edge
50
Distance from edge (m)
Fig. 5. Plant response to forest-clearcut edges 5 years after harvest (from HUGGARD and VYSE 2002a).
8
Making a difference
MASS, Sicamous Creek and several other similar projects in British Columbia have provided
extensive information on how management options affect many values in the short term at
the stand level. This information clearly forms the basis of science-informed management. It
is less clear that these experiments have actually affected management. The MASS project
has had a substantial impact on practices of one major company in coastal British Columbia,
but mostly as an operational demonstration of alternative practices, while the Sicamous
project has yet to have any major direct impact. This may have to do with differences in the
economic, social and ecological issues in coastal and interior forests. Clearcutting has been
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Al K. Mitchell et al.
ongoing on the coast for forty years, and on southeastern Vancouver Island, stands containing
old trees have largely been replaced with young managed stands. This has resulted in growing controversy, with highly active public groups in the nearby urban centres of Vancouver
and Victoria questioning the sustainability of even-aged management and demanding that
the practice of clearcutting be stopped. This threat to the social licence for harvesting on
public lands was recognized by MacMillan Bloedel (now Weyerhaeuser) and prompted the
announcement that the company would phase out clearcutting on their coastal operations in
favour of retention silvicultural systems. The role of the MASS Project in that decision was
to provide confidence that such systems could be used in coastal forests. Of primary importance were the findings that the systems tested at MASS could be safely and economically
implemented (BEESE and PHILLIPS 1998). The question of whether those systems are ecologically sound has been more difficult to address.
At Sicamous Creek, similar ecological information has been generated. However, in the
absence of a nearby large urban population, public concern for the ecological effects of
forestry is subdued, there is no international pressure, and the issue of stability for forestrydependent communities appears to have a greater impact than biodiversity issues in debates
about the management of public lands. Therefore, operations have changed little.
Acceptance of research results requires coincidence of ecological understanding, economic conditions and political realities (Fig. 6). Before research at MASS, industry economic
concerns were well known. However, intense public concerns were not well connected with
ecology or economics. Perhaps MASS contributed to a closer alignment of ecological and
economic factors, helping to suggest a way for industry to respond to intense public pressure.
Before Research
After Research
Industry economic
concerns well known
and well focused
Ecological
understanding
vague
Better ecological
understanding
I
E
E
Retention
Systems
P
MASS
Intense public
concerns not well
connected with
ecology or economics
Very little
ecological
knowledge
I
E
Sicamous Creek
Partial cutting
Systems
Vague public concerns
but some coincidence
with industry because of
dependent communities
P
Clearer coincidence
of ecological and
economic factors
I
Retention
Systems
P
Better public
understanding
Better
ecological
knowledge
Industry adopting
some methods
I
E
Partial cutting
Systems
P
No change in the public
Fig. 6. Influence of research on the interface between public (P), industry (I) and ecological (E) values.
For. Snow Landsc. Res. 78, 1/2 (2004)
149
This resulted in an increased public acceptance of changes in forestry practices and created a
niche for the application of scientific information to inform the debate on managing forests
for multiple values.
Before research at Sicamous Creek, very little ecological knowledge of the impacts of
silvicultural alternatives on subalpine forests was available. Public concern over forestry
practices was limited and associated with industry-dependent communities. After research,
ecological knowledge increased and industry adopted some methods where these coincided
with industry concerns (e.g., regeneration). However, there was little or no change in public
attitudes toward silvicultural alternatives.
9
Prospects for the future
Applied forest management is becoming more complex as concern over the management of
public lands and the number of resources to be considered increases. Long-term interdisciplinary applied forest ecological experiments such as MASS and Sicamous Creek are
providing information about complex responses of forest ecosystems to managed and natural
disturbances. Both projects have been remarkably successful in this respect over the first ten
years. Impressive lists of publications have been produced by the respective project collaborators through a combination of scientific cooperation, and common access to substantial
funding and facilities. But is this enough to retain long-term funding? If the current trend
toward results-based activities on publicly owned forests continues, research projects may be
judged only on their short-term influence. On this criterion, only the MASS project would
be judged a success. This would be difficult to accept since early results can often change in
the long term. In conclusion, (1) success may depend less on the information value of
applied ecological experiments and more on their short-term influence, and (2) the application of results depends as much or more on the coincidence of local economic and social
pressures as on the quality of the research.
Acknowledgements
The authors thank all the members of the MASS and Sicamous Creek project teams. Their studies
have enabled us to explore the influence of silvicultural alternatives on a wide range of values. We
also acknowledge funding from the Canada-British Columbia Forest Resource Development
Agreement (FRDA II), Forest Renewal BC (FRBC), and Forest Innovation Investment (FII).
Thanks to Weyerhaeuser British Columbia, Nanaimo Timberlands Services and Riverside Forest
Products for their operational support. Thanks also to C. Peterson (USDA, Forest Service) for his
kind invitation to prepare and present this paper.
10
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Accepted April 9, 2004